Screen mesh wick and method for producing the same

ABSTRACT

A screen mesh wick ( 14 ) and a method of making the same are disclosed. The wick is made separately and is adaptive for inserting into a heat pipe as a wick structure. The wick includes a plurality of elongated wires ( 141, 142 ) woven together and a plurality of protruding portions ( 145 ) formed on the wires. The protruding portions may be small metal powders attached to outer surfaces of the wires. The method includes the steps of weaving a plurality of wires to form a mesh ( 14 ′) firstly and then forming a plurality of protruding portions on the mesh, for example, by spreading the metal powders onto the mesh while the mesh is subject to heating. With these protruding portions formed on the wires, the effective pore size defined between the wires is reduced and therefore the wick is capable of providing a larger capillary pressure.

FIELD OF THE INVENTION

The present invention relates generally to an apparatus for transfer ordissipation of heat from heat-generating components such as electroniccomponents, and more particularly to a screen mesh wick applicable inheat pipes and a method for producing such wick.

DESCRIPTION OF RELATED ART

Heat pipes have excellent heat transfer performance due to their lowthermal resistance, and therefore are an effective means for transfer ordissipation of heat from heat sources. Currently, heat pipes are widelyused for removing heat from heat-generating components such as centralprocessing units (CPUs) of computers. A heat pipe is usually a vacuumcasing containing therein a working fluid, which is employed to carry,under phase transitions between liquid state and vapor state, thermalenergy from one section of the heat pipe (typically referring to as the“evaporating section”) to another section thereof (typically referringto as the “condensing section”). Preferably, a wick structure isprovided inside the heat pipe, lining an inner wall of the casing, fordrawing the working fluid back to the evaporating section after it iscondensed at the condensing section. Specifically, as the evaporatingsection of the heat pipe is maintained in thermal contact with aheat-generating component, the working fluid contained at theevaporating section absorbs heat generated by the heat-generatingcomponent and then turns into vapor. Due to the difference of vaporpressure between the two sections of the heat pipe, the generated vapormoves towards and carries the heat simultaneously to, the condensingsection where the vapor is condensed into liquid after releasing theheat into ambient environment by, for example, fins thermally contactingthe condensing section. Due to the difference of capillary pressuredeveloped by the wick structure between the two sections, the condensedliquid is then brought back by the wick structure to the evaporatingsection where it is again available for evaporation.

The wick structure currently available for heat pipes includes finegrooves integrally formed at the inner wall of the casing, screen meshor bundles of fiber inserted into the casing and typically held againstthe inner wall thereof, or sintered powder combined to the inner wall ofthe casing by sintering process. Among these wicks, the screen mesh wickis preferred to the other wicks due to its economic advantage inmanufacturing. The manufacture of a screen mesh wick is comparativelysimple and generally involves weaving together a plurality of pliablewires or threads such as metal wires or synthetic fibers. In this sense,the screen mesh wick is formed separately and then inserted into thecasing of a heat pipe.

In a heat pipe, the primary function of a wick is to draw condensedliquid back to the evaporating section of the heat pipe under thecapillary pressure developed by the wick. Therefore, whether the wickcould provide a large capillary pressure is a major consideration thatis used to evaluate the performance of the wick. A heat pipe with a wickthat has too large a pore size generally cannot provide a largecapillary force and therefore often suffers dry-out problem at theevaporating section as the condensed liquid cannot be timely sent backto the evaporating section of the heat pipe. Since it is well recognizedthat the capillary pressure of a wick increases due to a decrease inpore size of the wick, it is thus preferred to have the screen mesh wickwoven in a greater density so as to reduce the pore size formed betweenthe wires of the wick and accordingly obtain a relatively largecapillary pressure for the wick. However, under current weavingtechnology, it is difficult to reduce the pore size of the screen meshwick further due to the restriction of the weaving technology.

Therefore, it is desirable to provide a method for manufacturing ascreen mesh wick which can further reduce the pore size of the wick.What is also desirable is to provide a screen mesh wick made from thismethod and a heat pipe incorporating such wick.

SUMMARY OF INVENTION

The present invention relates in one aspect, to a screen mesh wick for aheat pipe. The screen mesh wick is made separately and is adaptive forinserting into a heat pipe as a wick structure. The screen mesh wickcomprises a plurality of elongated wires woven together and a pluralityof protruding portions formed on the wires. In one preferred embodiment,the protruding portions are small metal powders attached to outersurfaces of the wires. With these protruding portions formed on thewires, the effective pore size defined between the wires is reduced andas a result, the wick is capable of providing a larger capillarypressure for drawing liquid condensed at a condensing section of theheat pipe towards an evaporating section of the heat pipe.

The present invention relates in another aspect, to a method formanufacturing a screen mesh wick for a heat pipe, wherein the methodcomprises steps of forming a mesh firstly by weaving technology and thenforming a plurality of protruding portions on the mesh. By using thismethod, the capillary force that the wick could develop is increased asa result of a reduce in pore size of the mesh due to the presence of theprotruding portions, even though the weaving density of the mesh is notincreased.

Other advantages and novel features of the present invention will becomemore apparent from the following detailed description of preferredembodiment when taken in conjunction with the accompanying drawings, inwhich:

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of a heat pipe having a screen meshwick in accordance with one embodiment of the present invention;

FIG. 2 is an isometric view of the screen mesh wick of FIG. 1, being inan expanded status;

FIG. 3 is a top plan view of the screen mesh wick of FIG. 2;

FIG. 4 is an enlarged view of the circled portion IV of FIG. 3;

FIG. 5 is a flow chart showing a preferred method for manufacturing thescreen mesh wick of FIG. 2; and

FIGS. 6-7 are isometric views showing the steps of the preferred methodof FIG. 5 in manufacturing the screen mesh wick of FIG. 2.

DETAILED DESCRIPTION

FIG. 1 illustrates a heat pipe 10 in accordance with a preferredembodiment of the present invention. The heat pipe 10 includes a casing12 and a screen mesh wick 14 arranged against an inner wall of thecasing 12. The casing 12 is made of high thermally conductive materialsuch as copper or aluminum. Although the casing 12 as illustrated is ina round shape, it should be recognized that other shapes, such asrectangle or the like, may also be suitable. The screen mesh wick 14 isa porous structure and is saturated with a working fluid (not shown),which acts as a heat carrier when undergoing a phase transition fromliquid state to vaporous state. The working fluid is usually selectedfrom liquids—such as water or alcohol—that have a low boiling point andare compatible with the wick 14. In order to maintain the wick 14 totightly engage the inner wall of the casing 12, retaining means such asa helical spring (not shown) may be used to hold the wick 14 against thecasing 12.

The screen mesh wick 14 is typically made separately and then is rolledand inserted into the heat pipe 10 as a wick structure. Referring toFIGS. 2-4, the screen mesh wick 14 is formed by weaving together aplurality of flexible wires or threads such as metal wires or syntheticfibers. As illustrated in this embodiment, the wick 14 is constructed byweaving a first wire 141 and a second wire 142 together, wherein thefirst wire 141 has plate-type configuration while the second wire 142has a rod configuration. The wires 141, 142 have sufficient flexibilityso that they can be woven together easily. Each of the wires 141, 142has a preferred diameter or width of 45 micrometers (μm), and may beconstructed from a material with excellent thermal conductivity such ascopper, aluminum, or stainless steel. The wires 141, 142 may beconstructed from a single material or different materials, and also mayhave identical configurations or different configurations.

As shown in FIG. 4, a pore 143 is illustrated as defined between a pairof adjacent first wires 141 and a pair of adjacent second wires 142. Inorder to reduce the size of the pores 143 and ultimately gain arelatively large capillary pressure for the screen mesh wick 14, aplurality of micron-sized protruding portions 145 is combined to outersurfaces of the wires 141, 142. Some the protruding portions 145protrude into the pores 143 to reduce the size thereof. These protrudingportions 145 may be small particles such as metal powders that areattached to the wires 141, 142 after the wires 141, 142 are heated to atemperature near one-third to two-third of their melting point. Theseparticles may be such materials as copper, aluminum, stainless steel orcombination thereof, and may have an average particle size that is aboutone-fifth to one-third of the diameter or width of the wires 141, 142.Preferably, the melting points of these particles are not higher thanthose of the wires 141, 142. More preferably, the protrusions 145 andthe wires 141, 142 are made of the same metal.

With reference to FIG. 5, a preferred method 100 for constructing suchwick 14 is shown. The preferred method 100 generally includes two steps,i.e., the first step 101 and the second step 102. The first step 101 isto form a mesh 14′ by weaving together a plurality of the first andsecond wires 141, 142, as shown in FIG. 6. The second step 102 is toform a plurality of the protruding portions 145 on the outer surfaces ofthe mesh 14′ formed by the foregoing first step 101, to thereby obtainthe screen mesh wick 14 as illustrated in FIG. 2. As with the secondstep 102, if these protruding portions 145 to be formed on the mesh 14′are small metal powders, a nozzle 20 is typically used to spread thesemetal particles onto the mesh 14′ while the mesh 14′ is heated, forexample, to a temperature substantially equal to one-third to two-thirdof the melting point of the mesh 14′, thus combining these particles tothe mesh 14′ after these particles and the mesh 14′ are cooled. Forcombining these particles to the mesh 14′, some other methods may alsobe suitable. For example, the metal particles to be formed as theprotruding portions 145 of the wick 14 may be spread on a flat surfaceevenly to form a “bed of powder” in advance, and then the mesh 14′,after it is heated, is applied to the bed of powder, optimally with adownward pressing force, to thereby adhere the particles to the mesh 14′and form the screen mesh wick 14.

In the above-illustrated embodiment, the wick 14 is formed firstly byweaving technology and is then processed to further reduce the effectivepore size thereof by means of forming a plurality of the protrudingportions 145 thereon. The wick 14 is thus capable of providing a largercapillary force than the mesh without the protruding portions thereon,thereby effectively solving the dry-out problem as experienced by theprior art.

It is to be understood, however, that even though numerouscharacteristics and advantages of the present invention have been setforth in the foregoing description, together with details of thestructure and function of the invention, the disclosure is illustrativeonly, and changes may be made in detail, especially in matters of shape,size, and arrangement of parts within the principles of the invention tothe full extent indicated by the broad general meaning of the terms inwhich the appended claims are expressed.

1. A screen mesh wick being made separately and adaptive for insertinginto a heat pipe as a wick structure, the screen mesh wick comprising aplurality of elongated wires woven together and a plurality ofprotruding portions formed on the wires.
 2. The wick of claim 1, whereinthe protruding portions are small powders attached to outer surfaces ofthe wires.
 3. The method of claim 2, wherein the wires are flexible andare constructed from a single material or different materials.
 4. Thewick of claim 3, wherein the protruding portions are formed frommaterials including copper, aluminum, stainless steel and combinationsthereof.
 5. The wick of claim 4, wherein the melting points of the wiresare higher than those of the small powders.
 6. The wick of claim 3,wherein the wires are formed from materials including copper, aluminum,stainless steel and combinations thereof.
 7. The wick of claim 2,wherein the small powders have an average particles size that issubstantially one-fifth to one-third of a diameter or a width of thewires.
 8. The wick of claim 1, wherein the wires includes a first wirehaving a plate-type configuration and a second wire having a rodconfiguration.
 9. A method for manufacturing a screen mesh wick for aheat pipe comprising the steps of: forming a mesh by weaving technology;and forming a plurality of protruding portions on the mesh.
 10. Themethod of claim 9, wherein the mesh is formed by weaving a plurality offlexible wires that are constructed from a single material or differentmaterials.
 11. The method of claim 10, wherein the protruding portionsare formed by spreading small powders onto the mesh while the mesh isheated.
 12. The method of claim 11, wherein the melting points of thewires are higher than those of the small powders.
 13. The method ofclaim 10, wherein the protruding portions formed on the mesh are smallpowders, and the small powders are combined to the mesh by applying themesh to the small powders after the mesh is heated.
 14. The method ofclaim 13, wherein the melting points of the wires are higher than thoseof the small powders.
 15. A screen mesh wick being inserted into a heatpipe for transmitting heat from one end to another end thereof,comprising: a mesh made of wires woven together, the mesh defining aplurality of pores between the wires; and a plurality of protrusionshaving a size smaller than that of the wires, secured to the wires andprotruding into the pores prior to insertion into the heat pipe.
 16. Thescreen mesh wick of claim 15, wherein the protrusions are made ofpowders.
 17. The screen mesh wick of claim 15, wherein the wires have arod-shaped configuration and a flat-plate configuration.
 18. The screenmesh wick of claim 16, wherein the powders are made of a metal of one ofcopper, aluminum and stainless steel.
 19. The screen mesh wick of claim16, wherein the powders have a diameter which is about one-fifth toone-third of a diameter of the wires.
 20. The screen mesh wick of claim15, wherein the protrusions are secured to outer surfaces of the wires.